As President Bill Clinton recently discovered, there is no more complex and emotional issue in Christendom than Communion.

This issue is even more divisive than church issues linked to sexuality, which always grab headlines. The reality is that today's doctrinal earthquakes about sex are only important to the degree that they crack the rock on which altars stand. Churches argue about sex. Churches split over issues linked to Communion.

Cardinal John O'Connor of New York urged his listeners to see the big picture, as he explained why President Bill Clinton, a Southern Baptist, and Hillary Rodham Clinton, a United Methodist, should not have received Holy Communion in a Catholic parish in South Africa.

"The Eucharist is the sum and summary of our faith," said O'Connor, speaking on Palm Sunday at St. Patrick's Cathedral. "Holy Communion means not only our union with Christ in the Eucharist, but our union with other Catholics holding the same beliefs. ... To receive Holy Communion in the Catholic Church means that one believes one is receiving, not only a symbol of Christ, but Christ Jesus Himself."

When it comes to Catholic teachings about sacraments, he said, there is a controlling legal authority that gets to make and interpret the laws. Except under extreme circumstances, Communion is reserved for those who faithfully follow the teachings of the Roman Catholic Church. This high standard, noted O'Connor, should be a hurdle for millions of unrepentant and unorthodox Catholics, as well as non-Catholics.

This issue lurks behind many bitter squabbles. Many ask the obvious question: Are all of these Catholics really in Communion with one another and with Rome?

Catholics are not alone. Many United Methodists wonder if they should be in Communion with bishops and pastors who reject church teachings that sex outside of marriage is a sin. In the Presbyterian Church (U.S.A.), some liberal administrators and educators wonder if they should stay on board after the defeat of a law offering more flexibility for gays and lesbians. Many Episcopalians wonder if they should remain in Communion with bishops who embrace or refuse to condemn rites that honor gods other than the God of the Bible or who reject or redefine core doctrines such as the resurrection. The list goes on and on. These days, even Southern Baptists face occasional fights over sexuality.

Can anyone draw doctrinal boundaries in an age that welcomes spirituality, but not doctrine? President Clinton became a symbol of these disputes as he knelt to receive Communion in a church whose teachings he often actively opposes.

Meanwhile, it remains unclear exactly what happened on March 29 at Soweto's Regina Mundi Church. White House officials insist that they asked in advance whether the Clintons could receive Communion and were assured that they could, because of a "more ecumenical" policy adopted by the South African Conference of Bishops. The president's staff said the priest, Father Mohlomi Makobane, gave his blessing beforehand.

But the priest -- whose sermon in this Mass focused on the sin of adultery -- remembers the encounter differently. The result is a confusing "they said, he said" conflict. Father Makobane said he was told that the president probably would not receive Communion. The priest told reporters he was surprised when the Clintons came forward to receive the sacrament.

"Here you have the most powerful man in the world, and I can't embarrass Mr. Clinton by saying, "No, you go and sit down,' " he said.

The Vatican appears to be seeking clarity about what South African bishops have or have not said. But O'Connor and others have stressed that this is irrelevant, because regional bishops cannot override centuries of church tradition and explicit Vatican directives.

McCurry said the Clintons received Communion in the spirit of the prayer by Jesus recorded in John 17:21. This New Testament passage reads: "That all may be one, even as thou, Father, in me and I in thee, that they also may be one in us, that the world may believe that thou hast sent me."